1. Field of the Invention
The present invention relates to a colored curable composition, a colored pattern formed using such a colored curable composition, and a color filter provided with the colored pattern.
2. Description of the Related Art
A color filter is manufactured by forming, using a photolithographic method, an ink-jet method, or the like, a colored pattern and a black matrix made with colored curable compositions that include a pigment dispersion composition, in which an organic pigment or an inorganic pigment is dispersed, a polymerizable compound, a polymerization initiator, an alkali soluble resin, and other components.
Recently, color filters are not only being used in liquid crystal display (LCD) elements for monitor applications, but applications thereof are also expanding to televisions (TVs). Accompanying such expansion in applications has been a desire for improvements in productivity, in order to be able to efficiently manufacture color filters having a large surface area. For this reason, slit coating methods have become the main coating method used for forming the colored patterns of color resists, in place of general-purpose spin coating. If dry matter of a curable composition adheres and accumulates on a slit coating head, when carrying out slit coating of a curable composition to a substrate surface during the mass production of panels of large surface area, then foreign matter defects would occur in the panels obtained therefrom. In order to prevent such occurrences, a coating head has been placed in a solvent atmosphere when on standby, or a nozzle cleaning mechanism has been provided and periodic washing has been carried out, as means to suppress the generation of foreign matter. However, these require a complicated process on the coating device side.
Further, in order to form a colored region with a curable composition, drying has been suppressed between formations of coated layers having specific surface areas, and good cleanability of uncured regions in dried coated layers has been desired. In order to improve the cleanability of the dry coated layers, it is necessary for a dry layer formed from a photo curable composition to be readily dissolved by the nozzle cleaning solvent and by the liquid of the curable composition supplied for coating.
The uniformity of dispersion of pigment as colorant in the curable composition also contributes greatly to the uniformity of the coated layer itself. Thus, a finer state of dispersion (good dispersibility) and more stable dispersion (good dispersion stability) has been desired for a pigment that is included in a colored curable composition. When the dispersibility of a pigment is insufficient, this may lead to a large amount of development residue (residue) on a substrate, to a reduction in chromaticity and dimensional precision of a manufactured color filter, or to a significant deterioration in the contrast thereof. When the dispersion stability of a pigment is insufficient, then, in particular, during the manufacturing processes of the color filter, the uniformity of layer thickness in the colored curable composition coating process may readily fall, the sensitivity in the exposure process may readily fall, and/or the alkali solubility in the development process may readily fall. When there is poor dispersion stability of the pigment, this may cause an aggregation of the composition components of the colored curable composition and cause a rise in viscosity with time, leading to an extremely short pot-life thereof.
Although it is effective to make the particle size of a pigment finer in order to improve coloring characteristics, such as the contrast of a color filter, since the surface area of the pigment particles becomes larger when the particle size of a pigment is made finer, the cohesive force between pigment particles becomes strong, and it has been difficult to achieve both a high level of dispersibility and a high level of dispersion stability.
The following techniques are known for making pigment particles finer and improving the dispersibility of pigment particles.
Generally, a method (salt milling method) is known for making the primary particles of a pigment finer by mechanically mixing and kneading, using a kneader or the like, a pigment, a water soluble inorganic salt, and a water soluble organic solvent which does not dissolve substantially such an inorganic salt. The primary particle mixture of the obtained fine pigment is added to water and agitated, using a mixer or the like, to form a slurry state. Next, by filtering this slurry, washing with water and drying, a fine pigment is obtained as a secondary aggregate, which is an aggregate of the primary particles of the pigment. The dispersion process in ordinary dispersion machines, such as a sand mill, a ball mill, or the like, is a process that loosens the secondary aggregate, which is an aggregate of the primary particles of pigment, obtaining a dispersion body that is close to the state of the primary particles.
However, as the primary particles of the pigment are made finer, aggregation readily occurs and an aggregate (secondary aggregate) is readily generated either in the slurry state or during drying. Strong secondary aggregation more readily occurs as the primary particles of a pigment become finer. Therefore, it has been generally very difficult to re-disperse back to primary particles a pigment that has been made fine. A color filter formed using a dispersion body in which a large amount of secondary aggregates exists not only has a large amount of light dispersion, and a significant reduction in contrast and has occurrences of color density unevenness, but also the cleanability and solubility of the un-cured layer thereof deteriorate due to aggregations of pigment. Therefore, it is desirable for a pigment dispersion composition to have primary particles that are dispersed stably without aggregating, as well as desirable for the pigment dispersion composition to have good handling characteristics.
With the objective of suppressing the strong secondary aggregation of such fine pigments, techniques are proposed for obtaining a high color contrast color filter using such a pigment dispersion by processing the pigment by adding a rosin or rosin derivative, or a nonaqueous-soluble monomer or oligomer, during salt mill processing (see, for example, Japanese Patent No. 3130217 and Japanese Patent Application Laid-Open (JP-A) No. 2004-233727). A technique is also proposed for obtaining a pigment dispersion composition excellent in dispersion stability by using a polymer compound having a heterocycle in a side chain thereof as a pigment dispersant in the dispersion process, and obtaining a colored photosensitive composition and high color contrast color filter using the same (see, for example, JP-A No. 2003-26950). However, from a practical point of view further improvements are desired in the dispersibility and dispersion stability of fine pigments.
Thus, in order to improve productivity in the mass production of LCD panels for large-sized TVs, improvements in the coatability of photosensitive compositions of dispersed pulverized pigments and fine pigment particles, and in addition improvements in cleanability of color resist dry layers formed with such photosensitive compositions, are important.